Could you show a screenshot of your events, please?
Common mistakes are using wrong slash if it's in a subfolder (pretty sure it's gotta be like "folder\splashsound"). This doesn't matter if you don't use folders though, if you have sounds at the base of the "sounds" folder, can just type "splashsound".
And also don't include the extension, so if you have splashsound.mp3, don't type ".mp3",just simply splashsound.